Gyroscopes have been used to measure rotation rates or changes in angular velocity about an axis of rotation. A basic conventional fiber optic gyroscope (FOG) includes a light source, a beam generating device, and a fiber optic coil coupled to the beam generating device that encircles an area. Rotation about the axis normal to the fiber optic coil either slows or speeds the propagation of the light through the coil, resulting in a measureable shift in phase of the light.
In an interferometric fiber optic gyroscope (IFOG), the light source is split into two beams that propagate in opposite directions through the fiber optic coil. After propagating through the coil, the two beams of light are recombined to compare the phase upon exit from the coil. Recombining the beam produces an interference pattern indicative of the phase of the respective beams. At a detector, shifts in the interference pattern are proportional to the phase difference between the two recombined beams. Measurement of the shifts in the interference pattern indicates a speed and direction of rotation about the axis of the coil.
The IFOG includes a number of fiber optic components that must be optically connected to form beam paths from the light source. Fusion splicing is used to operatively weld the optical components to form the necessary light paths. Fusion splicing and stowage processes add many manual process steps to IFOG manufacturing, thus having a significant contribution to IFOG cost along with that of the discrete optical components. Rather than fusion and manual assembly, there is a need, in the art, to exploit the automated methods of fabrication to produce an IFOG.
Silicon optical bench (SiOB) is an emerging technology that offers the capability of automated manufacturing of high density and highly functional optical systems in a very small package at low cost. SiOBs are optical benches formed from silicon or a similar semiconductor material. Troughs are etched in the silicon material, or substrate, using micro-fabrication processes, to hold the various optical components. The high accuracy of the micro-fabrication process allows the optical components and optical fibers to be precisely aligned relative to one another in the various troughs. The self-aligning quality of the optical components upon placement in a suitably formed silicon substrate allows for “passive alignment” of the components and reduces the need to actively ensure the various components are aligned with to suitably form an efficient optical path. Light may also be directed between the various optical components using free space optics such as lenses etc.
The benefits of SiOBs include lower cost of production as well as reduced size and mass due to wafer scale fabrication of the silicon optical bench together with enhanced gyroscope performance compared with conventional fabrication techniques. However, the SiOB technology has not been exploited in the context of more complex component such as the IFOG, but rather has been used for communications applications which are generally passive components.